Resilience of Organic Matter Recovery to Seasonal Temperature Changes in a Wastewater Treatment System Adopting the High-Rate Contact Stabilization Process

The high-rate contact stabilization–activated sludge (HiCS–AS) process, which integrates an upstream high-rate contact stabilization process with a downstream activated sludge process, is a promising approach for enhancing energy recovery from municipal wastewater. This 16-week continuous study evaluated the organic matter recovery capacity and process stability of a HiCS–AS process, configured as a sequencing batch reactor, under realistic conditions where water temperatures decreased from 29 °C to 14 °C. The upstream HiCS process, operating at a solids retention time of 0.60 days, exhibited stable sludge settling behavior and achieved a stable carbon recovery rate of 0.23 ± 0.04 g-COD/g-COD. The overall COD removal rate for the system was 86% ± 3%, and the HiCS–AS process demonstrated a statistically significant increase in organic matter recovery compared to a parallel single activated sludge process (paired Student’s t-test, p < 0.05). These findings indicate that the HiCS–AS process provides a consistent and effective approach to organic matter recovery compared to conventional processes.